Drying box and incubator



March 29, 1938. I H. BRUNING E' I' AL 2,112,731

7 DRYING BOX AND INCUBATOR Original Filed Sept, 28, 1955 2 Sheets-Sheet 1 March 29, 1938. H. BRUNING ET AL 2,112,731

DRYING BOX AND INCUBATOR Original Filed Sept. 28, 1935 2 Sheets-Sheet 2 3f 2/ JAAAAAAAKAAAAAAA L Patented Mar. 29, 1938 UNITED STATES- 2,112,731 DRYING BOX AND INCUBATOB Hans Briining many, assignors to and Otto Schiiller, Hanan, Gerthe firm of W. C. Heraens.

G. m. b. 11., Hanan, Germany Application September 28, 1935, Renewed November 8, 1937.

Serial No. 42,032. In Germany May 9 Claims. (Cl. $19-35) The present invention relates to drying boxes and incubators which are automatically regulated to maintain, with extreme exactness, any adjustable heat degrees at uniform heat distribution, and particularly refers to the shape and the regulating devices of such apparatus.

Laboratory-drying boxes and incubators generally used hitherto have the form of a four-sided prism and as a rule are protected by asbestos sheets against heat losses.

As with devices of a cylindrical form the ratio between outer surface and volume is smaller than with a prismatic form, the heat losses for equal volumes are smaller. The insulation may easily be effected by vitreous insulating material or the like, having better heat insulating properties than asbestos sheets, because the cylindrical inner and outer walls of the apparatus are self-supporting. Whereas with boxes of prismatic form uniform distribution of temperatures offers serious difflculties, as the heating wires must be stretched upon. tubes .or frames arranged at the bottom, with a cylindrical form uniform heating of the space may easily be obtained by arranging, in a suitable manner, the heating wires in the form of small mica heating units around the cylindrical space. By arranging the heating elements near the door and at the lower half of theapparatus closer together than at other places and by using aluminiumor copper-sheet as material for the inner wall, uniformity of temperature of :1 C. may easily be obtained within the whole space. The shelves or insertion plates are carried by a frame which may be removed by a simple operation, so that the inner wall of the box and all inner. parts may easily be cleaned.

In the accompanying drawings, a construction according to the invention is shown by way of example.

Fig.1 shows a front elevation of a drying box according to the invention, partly in cross section and partly broken away.

Fig. 2 shows a central longitudinal section through the device illustrated in Fig. 1,

Fig. 2a is a detail view,

Fig. 3 is a section on line 3-4 of Fig. 2,

Figs: 4 and 5 are diagrammatic cross sectional views showing two modified forms of construc-- tion of the invention,

Figs. 6 and 7 are diagrammatic illustrations of curves illustrating the action of the invention with respect to regulation.

The drying box or incubator shown in Figs. 1-8 rests upon a foot or support I and comprises an inner and an outer cylindrical wall of sheet metal 2 and 3 respectively both of which are closed by a bottom 4 and 5 respectively, preferably forming part of the corresponding wall. The inner cylindrical member 2 consists of sheet metal of high coeflicient of thermal expansion, surrounds the useful space i of the apparatus and carries a series of mica heating units I. The wall 2 is insulated against the outer wall I by vitreous insulating material 8 or the like. A door I hinged at Ill and insulated also by vitreous insu- 10 dating material II or the'like serves to close the apparatus. A frame l2, fitting the useful space i, may easily be withdrawn and serves to carry plates it upon which material or the likev to be treated may be arranged. In the lowest portion of the walls 2 and; an opening is provided and these openings are connected by a tube It through which liquid may be drained off in case a vessel breaks inside the apparatus. The tube i4 simultaneously serves to introduce air into the space t. Diametrically opposite the tube It a similar tube II is provided also extending from the useful space 0 to the outside, where it opens into a socket l6 adapted to receive a thermometer II which extends into the useful space 6 andserves to indicate the temperature within the apparatus. In the cylindrical portion of the socket it openings. II are provided throughwhich damp air may escape to the atmosphere.

In drying boxes used hitherto the regulation of the temperature is effected by an inwardly projecting and exposed thermostat responsive to the temperature within the useful space and controlling a relay. In such regulating arrangements the heat is transferred from the heating elements to the-wall of the useful space, frorn said wall to the air in the useful space and from the air to-the feeler.

According to the invention, however, in cylin-. drlcal drying boxes the thermal expansion of the sheet metal member, surrounding the useful space, with regard to a rod of low coefficient of thermal expansionis used to regulate the temperature. As with the novel arrangement the wall of the useful space itself serves as regulating member, i. e., the path of heat transfer is considerably shortened, an extremely frequent action of the regulating device and thereby a temperature regulation of considerably higher precision results.

It is well known already to regulate electrically heated tube stoves and heating plates by using the expansion of a portion of the wall, however, it is not known hitherto to use the thermal expansion of a portion of a wall with regard to a rod-shaped body, arranged outside the useful as proved, that by multaneously space of drying boxes and incubators, to eifect regulation of such devices, probably because inexactnesses were expected on account of bulgings of the thin walls and particularly on account of the fact, that no favored expansion'of these walls occurs in any direction. Strong prejudices were to be cast off to use the known principle also in connection with drying boxes and incubators, be-

cause an exact or precise regulation was not to be foreseen. Thorough tests, however, have using the known regulating principle in connection with drying boxes and incubators of a cylindrical shape, a considerably better and more precise regulation is obtained than has been possible hitherto with the use of immersed feelers. A further important advantage of the novel regulating device consists in this, that troubles are avoided which are caused by the action of corrosive gases upon the-feeler or by bendings, of the latter. The regulating device according to the novel arrangement is perfectly protected and lies entirely outside the useful space of the box or incubator. By omittingthe usual feeler within the apparatus simultaneously the available space may be better utilized.

If, in cases in which a directly heated is used for the regulation, the regulation of the temperature is to be further improved, the portion of the wall in questionmay be provided with an auxiliary heating coil, operating in accordance with the main heating coil. The improvement is based upon the idea to effect an earlier response of the regulating device than would be the case with heat transfer by heat conduction through the cover of the useful space and by air convection within the useful space. As has beenshown by tests, during the switching off period in which the auxiliary heating coil also is rendered currentless, complete compensation results between the temperature of the useful space and that of the wall, so that switching on of the current again is always'effected at the same temperature. By shortening the heating period, the effect is obtained, that the regulator still more frequently operates than otherwise and therefore the regulating curve of the device is further improv v The heating period may, by suitably proportioning the heating efiect of the auxiliary heating, be shortened as desired. Of course, this shortening is not allowed to be carried on so far, 1. e. the temperature of the regulator is not allowed to so strongly lead thetemperature of the box or incubator, that the amount of heat, supplied during the heating period to the box or incubator, is, not sufilcient to compensate for the idle losses at the adjusted temperature. It has been found, that the upper limit for the heating eifect of the auxiliary heating lies at about 15% of the capacity of the supply If an auxiliary heating is to be provided on P rticularly thin walls of sheet metal such as a paper thin'wall, such walls are preferably reinforced by a flat or profiled strip of the wall metal and the auxiliary heating'coil is then arranged upon this strip. Preferably the strip siserves in such cases as expansion element for operating the regulating contact.

strip is riveted or soldered to the bottom 4 of paratus which is not directly heated.

may best be seen from Fig. 3, a U-shaped 29 of sheet metal, serving as reinforcement,

In this U-shaped strip 29 auxiliary heating coils 2| and connected to each other by a wire 29 and surrounding the rod |9, are arranged. The rod l9 portion of the wall'not contacts 29 and 39 are described and shown of low coefilcient of thermal expansion preferably is fixed at 24 to the strip 29 itself. The free ends of the auxiliary heating coils 2| and 22 are, by wires 25 and 26 respectively connected to the heating elements 'I' which in turnare connected by wires 21 and 29 to contacts 29 and 39 (Figs 2 and 2a), forming part of a heating circuit supplied with current by any suitable source of powor not shown in the drawings. Other parts of the heating circuit, as switches, relays, control lamps and so on, are also not shown in the drawings, as they do not form part of the invention. The carried by arms 3| and 32 respectively. The arm 32 may, by means of a spindle 93 provided with a knob 34, be adjusted with regard to the arm 3|, thus pressing the contacts 29 and more or less firmly together, depending on the temperature desired to be obtained within the space 6. The other .arm 9|, carrying the contact 29, is swingably arranged and connected to the free end of the rod l9.

When the drying box or incubator is heated, the rear wall or bottom 4 expands, whereas the rod l9 retains about its original length. At a certain temperature, the freeend of the rod l9 disengages the contact 29 from the countercontact 39, whereby the heating circuit is opened. .Upon the now following cooling of the box, the bottom 4 contracts and the end of the rod I9 allows the-contact 9 to again approach its counter-contact 30, until he contacts 29, 39 and thereby the hating circuit are closed again.

Fig. 4 diagrammatically shows another construction of the regulating arrangement. In this case also the wall 2 of-the useful space 9 of the drying box consists of a metal of high coefficient of thermal expansion and is surrounded by a series of heating'elements 1. Parallel to the longitudinal axis of the apparatus and-between the cylindrical walls 2 and 3 a rod I 9 is arranged which-again consists of material of low coeflicient of thermal expansion. One end 39 of the rod is is connected to the cylindrical wall 2 surrounding the useful space 6. The free-end of the rod l9 extends through a hole in the arm II which is swingably arranged and'carries the contact 29 connected to the heating circuit. The countercontact 99 cooperating with the contact 29, is carried by the spindle 99 with knob 34, may be brought in predetermined positions, corresponding to thetemperatures which are desired within the space 9.

The operation of this device is the same as described with reference to the apparatus shown in Figs. 1-3.

According to a further modificatiomia tubelike feeler provided with an auxiliary heating coil "may, A surrounding the useful space '6, be'immersed into the interior of the box or incubator and be used for the fine regulation. The coil 98 is well isolated from the tube 35 and the rod II which it diference, however, that in the apparatus, 'iust of the thermal expansion between the tube ii and the rod l9 which is used tocontrol the con tacts '29 and 99. The additional heating which is known already for regulators consisting of himetal, has, however, hitherto never been used the arm 92 which, by means of ll and tothe arm,

in'Fig. 5, it is the difference without connection with the wall 2 in connection with expansion regulators comprising a rod.

The eiiect obtained by the regulation may be seen from the'regulating curves diagrammatically indicated in Figs. 4 and 5. Fig. 4 shows the regulating curve of a'box having the heating coil arranged at the outside and provided with a closed inner space into which immerses the-ieeler having no auxiliary heating coil. Fig. 5 shows the regulating curve 01' a box of equal construction in which the teeleris heated by an auxiliary heating coil. In both cases the heatingand cooling curves have the same inclination towards the abscissa, also the switching-on temperature is the same in both cases. The time of the switching periods, however, is diilerently long from which follows the higher exactness of regulation by the use of the additionally heated regulator.

What we claim is;

1. In an electrically'heated receptacle for providing a chamber having a substantially constant temperature, the combination of a receptacle having a cylindrical side wall-and having end walls, one of said end walls constituting a closure, said receptacle being constructed of metal having a high coefllcient of thermal expansion, with an insulating covering for said receptacle andan enclosure for said insulating covering, electrical heating elements located outside said receptacle and inside said'insulating covering, an element having a low coeflicient of thermal expansion located outside said receptacle and having one end fixedly secured to said receptacle adjacent one edge of the cylindrical wall, a circuit maker and breaker for controlling said heating elements and carried by said receptacle at a point spaced from the fixed end oi said element, and'an operative mechanical connection between the other end oi. said element and said circuit maker and breaker whereby substantially uniform temperature is maintained in said receptacle, said receptacle having an auxiliary heating coil controlled by said circuit maker and breaker and arranged primarily for heating that part of the receptacle between the points of attachment of said element and of said circuit maker and breaker, whereby the time lag in the action of the circuit. maker and breaker responsive to changes in temperature is diminished. a

2. In an electrically heated receptacle for providing a chamber having a substantially constant temperature, the combination of a receptacle having a cylindrical side wall and having end walls, one oi said end walls constituting a closure, said receptacle being constructed oi metal having a high coefiicient of thermal expansion, with an insulating covering for said receptacle and an enclosure for said insulating covering, electrical heating elements located outside said receptacle and inside said insulating covering, an element having a low coefllcient of thermal expansion located outside said receptacle and having one end fixedly secured to said receptacle adjacent one edge oilthe cylindrical wall, a circuit maker and breaker for controlling said heating elements and carried by said receptacle at a .point spaced from the fixed end of saidelement, and an operative mechanical connection between the other end of said element and said circuit maker and breaker whereby substantially uniform temperature is maintained in said receptacle. said element extending diametrically across 7 one end wall of said receptacle and said receptacle having an auxiliary heating coil controlled by said circuit maker and breaker and arranged primariuously adjusting the point of actuation of said circuit maker and breaker whereby any operating temperature may be selected and maintained ithin a predetermined rangepi temperatures.

4. In an electrically heated receptacle for providing a chamber having a substantially constant temperature, the combination of a receptacle having a cylindrical side wall and having end walls, one of said end walls constituting aclosure, said receptacle being constructed of metal having a high coeflicient oi thermal expansion, with an insulating covering for said receptacle and an enclosure ior said insulating covering, electrical heating elements located inside said insulating covering, an element having a low coeiilcient of thermal expansion carried by said receptacle and having one end fixedly secured to said receptacle adjacent one edge or the cylindricalwall, a .circuit maker and breaker having a movable contact carrying arm for controlling said heating eleinents and carried by said receptacle at a point spaced from the fixed end of said element, and an operative mechanical connection between the other end of said element and said circuit maker and breaker whereby substantially uniform temperature is maintained in said receptacle, said element having a direct mechanical engagement with said arm to eliminate backlash in the actuation of said circuit maker and breaker.

5. A device as claimed in claim 4 in which said element slidably engages said arm and said element has a shoulder for actuating said arm.

6. In an electrically heated receptacle for providing a chamber having a substantially constant temperature, the combination of a support with a receptacle having a ,cylindrical side wall and having end walls, said receptacle having its axis extending substantially horizontallyand one of said end walls constituting a closure, said receptacle being constructed of metal having a high coeificient of thermal expansion, with an insulating covering for said receptacle and an enclosure for said insulating covering, electrical heating elements located outside said receptacle and inside said insulating covering, an element having a low coefiicient of thermal expansion located outside said receptacle and having one end fixedly secured to said receptacle adjacent one breaker for controlling said heating elements and carried by said receptacle at a point spaced from the fixed endof said element, and an operative mechanical connection between the other end of said element and said circuit maker and breaker whereby substantially uniform temperature is maintained in said receptacle, said circuit maker and breaker being located outside said insulation and said element extending through said insulation to said circuit maker and breaker.

7- A device as claimed in claim 4 in which the end wall of said receptacle between said fixed end of said element and said circuit maker and breaker is reinforced with a member having substantially the same coefllcient of thermal expansion as said receptacle.

8. In an electrically heated receptacle for providing a chamber having a substantially constant temperature, the combination of a receptacle having side walls and having end-walls, one of said walls constituting a closure, said receptacle being constructed of metal having a high coemcient of thermal expansion, with an insulating covering for said receptacle and an enclosure for said insulating covering, electrical heatingelements .10-

' cated inside said insulating covering, an element having a low coeflicient of thermal expansion carried by said receptacle and having one end fixedly secured to said receptacle adjacent one edge of an outer wall, a circuit maker and breaker having a movable contact carrying arm for controlling said heating elements and carried by said receptacle at a point spaced from the fixed end of said element, and an operative mechanical connection between the other end of said element and said circuit maker and breaker whereby substantially uniform temperature is maintained in said receptacle, said element having a direct mechanical engagement with said arm to eliminate backlash in the actuation of said circuitmaker and breaker.

9. A device as claimed in claim 8 in which said circuit maker and breaker has means for continuousiy adjusting the point of actuation of said circuit maker and breaker whereby any operating temperature may be selected and maintainedwithin a predetermined range of temperatures.

HANS BRtiNING. o'rro SCHULLER 

